scholarly journals Mid-pliocene Atlantic Meridional Overturning Circulation not unlike modern

2013 ◽  
Vol 9 (4) ◽  
pp. 1495-1504 ◽  
Author(s):  
Z.-S. Zhang ◽  
K. H. Nisancioglu ◽  
M. A. Chandler ◽  
A. M. Haywood ◽  
B. L. Otto-Bliesner ◽  
...  
Keyword(s):  
Heat Transport ◽  
Climate Models ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Transport ◽  
Overturning Circulation ◽  
Consistent Change ◽  
Intercomparison Project ◽  
Meridional Overturning ◽  
Consistent Increase

Abstract. In the Pliocene Model Intercomparison Project (PlioMIP), eight state-of-the-art coupled climate models have simulated the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), northward ocean heat transport and ocean stratification simulated with these models. None of the models participating in PlioMIP simulates a strong mid-Pliocene AMOC as suggested by earlier proxy studies. Rather, there is no consistent increase in AMOC maximum among the PlioMIP models. The only consistent change in AMOC is a shoaling of the overturning cell in the Atlantic, and a reduced influence of North Atlantic Deep Water (NADW) at depth in the basin. Furthermore, the simulated mid-Pliocene Atlantic northward heat transport is similar to the pre-industrial. These simulations demonstrate that the reconstructed high-latitude mid-Pliocene warming can not be explained as a direct response to an intensification of AMOC and concomitant increase in northward ocean heat transport by the Atlantic.

scholarly journals Mid-pliocene Atlantic meridional overturning circulation not unlike modern?

2013 ◽  
Vol 9 (2) ◽  
pp. 1297-1319 ◽  
Author(s):  
Z.-S. Zhang ◽  
K. H. Nisancioglu ◽  
M. A. Chandler ◽  
A. M. Haywood ◽  
B. L. Otto-Bliesner ◽  
...  
Keyword(s):  
Heat Transport ◽  
Climate Models ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Transport ◽  
Overturning Circulation ◽  
Consistent Change ◽  
Intercomparison Project ◽  
Meridional Overturning ◽  
Consistent Increase

Abstract. In the Pliocene Model Intercomparison Project (PlioMIP), eight state-of-the-art coupled climate models have simulated the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), northward ocean heat transport and ocean stratification simulated with these models. None of the models participating in the PlioMIP simulates a strong mid-Pliocene AMOC as suggested by earlier proxy studies. Rather, there is no consistent increase in AMOC maximum among the PlioMIP models. The only consistent change in AMOC is a shoaling of the overturning cell in the Atlantic, and a reduced influence of North Atlantic Deep Water (NADW) at depth in the basin. Furthermore, the simulated mid-Pliocene Atlantic northward heat transport is similar to the pre-industrial. These simulations demonstrate that the reconstructed high latitude mid-Pliocene warming can not be explained as a direct response to an intensification of AMOC and concomitant increase in northward ocean heat transport by the Atlantic.

scholarly journals Southern Ocean Heat Uptake, Redistribution, and Storage in a Warming Climate: The Role of Meridional Overturning Circulation

2018 ◽  
Vol 31 (12) ◽  
pp. 4727-4743 ◽  
Author(s):  
Wei Liu ◽  
Jian Lu ◽  
Shang-Ping Xie ◽  
Alexey Fedorov
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Climate Models ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
The Other ◽  
Anthropogenic Heat ◽  
Overturning Circulation ◽  
Ocean Heat Uptake ◽  
Meridional Overturning

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO2 enters the Southern Ocean near 60°S and is stored around 45°S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO2 increase into two major components: one due to wind changes and the other due to direct CO2 effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60°S coupled to a surface heat flux increase. In contrast, at 45°S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46°S at a rate of 0.07 ZJ yr−1 (° lat)−1 (1 ZJ = 1021 J), contributing 20% to the total OHS maximum. The direct CO2 effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42°S at a rate of 0.30 ZJ yr−1 (° lat)−1, accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO2 effect, and does not compensate the intensified Deacon cell.

The Effect of Arctic Freshwater Pathways on North Atlantic Convection and the Atlantic Meridional Overturning Circulation

2018 ◽  
Vol 31 (13) ◽  
pp. 5165-5188 ◽  
Author(s):  
He Wang ◽  
Sonya Legg ◽  
Robert Hallberg
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Deep Convection ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning

This study examines the relative roles of the Arctic freshwater exported via different pathways on deep convection in the North Atlantic and the Atlantic meridional overturning circulation (AMOC). Deep water feeding the lower branch of the AMOC is formed in several North Atlantic marginal seas, including the Labrador Sea, Irminger Sea, and the Nordic seas, where deep convection can potentially be inhibited by surface freshwater exported from the Arctic. The sensitivity of the AMOC and North Atlantic to two major freshwater pathways on either side of Greenland is studied using numerical experiments. Freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes. The sensitivity experiments are performed in two sets of models (CM2G and CM2M) with different control simulation climatology for comparison. Freshwater via the route east of Greenland is found to have a larger direct impact on Labrador Sea convection. In response to the changes of freshwater route, North Atlantic convection outside of the Labrador Sea changes in the opposite sense to the Labrador Sea. The response of the AMOC is found to be sensitive to both the model formulation and mean-state climate.

scholarly journals Frequency Domain Multimodel Analysis of the Response of Atlantic Meridional Overturning Circulation to Surface Forcing

2013 ◽  
Vol 26 (21) ◽  
pp. 8323-8340 ◽  
Author(s):  
Douglas G. MacMartin ◽  
Eli Tziperman ◽  
Laure Zanna
Keyword(s):  
Frequency Domain ◽  
Climate Models ◽  
Transfer Functions ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Model Errors ◽  
Overturning Circulation ◽  
Model Version ◽  
Spectral Peaks ◽  
Meridional Overturning

Abstract The dynamics of the Atlantic meridional overturning circulation (AMOC) vary considerably among different climate models; for example, some models show clear peaks in their power spectra while others do not. To elucidate these model differences, transfer functions are used to estimate the frequency domain relationship between surface forcing fields, including sea surface temperature, salinity, and wind stress, and the resulting AMOC response. These are estimated from the outputs of the Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 3 (CMIP3) control runs for eight different models, with a specific focus on Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (GFDL CM2.1), and the Community Climate System Model, version 4 (CCSM4), which exhibit rather different spectral behavior. The transfer functions show very little agreement among models for any of the pairs of variables considered, suggesting the existence of systematic model errors and that considerable uncertainty in the simulation of AMOC in current climate models remains. However, a robust feature of the frequency domain analysis is that models with spectral peaks in their AMOC correspond to those in which AMOC variability is more strongly excited by high-latitude surface perturbations that have periods corresponding to the frequency of the spectral peaks. This explains why different models exhibit such different AMOC variability. These differences would not be evident without using a method that explicitly computes the frequency dependence rather than a priori assuming a particular functional form. Finally, transfer functions are used to evaluate two proposed physical mechanisms for model differences in AMOC variability: differences in Labrador Sea stratification and excitation by westward-propagating subsurface Rossby waves.

Ocean Heat Transport’s Response to Future Climate Projections

2021 ◽  
Author(s):  
Jennifer Mecking ◽  
Sybren Drijfhout
Keyword(s):  
Heat Transport ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Future Climate ◽  
Pacific Basin ◽  
Climate Projections ◽  
Ocean Heat Transport ◽  
Atlantic Basin ◽  
Meridional Overturning ◽  
Future Climate Projections

<p>This study investigates the response of the meridional Ocean Heat Transports (OHT) to future climate projections in both CMIP5 and CMIP6 models.  Globally the OHT transport is declining/becoming more southward across all latitudes in the Northern Hemisphere, while at latitudes south of 10°S the OHT is icreasing/becoming more northward.  These changes in OHT are much stronger in CMIP6 models relative to CMIP5, especially for the rcp2.6/ssp126 scenario relative to the rcp85/ssp585 scenario.   Throughout the entire Atlantic basin the northward heat transport is reduced and can be tied to the velocity driven overturning (Atlantic Meridional Overturning Circulation (AMOC)) contribution to the OHT.  While the temperature driven changes in the Atlantic basin dampen the changes in the OHT.  In the Indo-Pacific basin the OHT transport north of the equator does not change much since the temperature and velocity driven changes balance each other.   However, south of the equator the increase in northward heat transport is caused by the overturning velocity driven changes and again dampened by temperature driven changes.  These changes in the Indo-Pacific basin can be tied to changes in wind driven subtropical overturning cells.</p>

scholarly journals Does the Atlantic Multidecadal Oscillation Get Its Predictability from the Atlantic Meridional Overturning Circulation?

2016 ◽  
Vol 29 (14) ◽  
pp. 5267-5280 ◽  
Author(s):  
Laurie Trenary ◽  
Timothy DelSole
Keyword(s):  
Time Scales ◽  
Autoregressive Model ◽  
Climate Models ◽  
Optimization Technique ◽  
Atlantic Multidecadal Oscillation ◽  
Atlantic Meridional Overturning Circulation ◽  
Statistical Optimization ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Meridional Overturning

Abstract This paper investigates the predictive relation between the Atlantic multidecadal oscillation (AMO) and Atlantic meridional overturning circulation across different climate models. Three overturning patterns that are significantly coupled to the AMO on interannual time scales across all climate models are identified using a statistical optimization technique. Including these structures in an autoregressive model extends AMO predictability by 2–9 years, relative to an autoregressive model without these structures.

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